It has long been known that it is possible to induce a current in a circuit without a physical connection to that circuit using the principle of magnetic resonance. Resonance is the tendency of a system to oscillate with larger amplitude at some frequencies than others. These frequencies are known as the system's resonant frequencies. At these frequencies, even small periodic driving forces can produce large amplitude oscillations, because the system stores energy. It has been shown that it is possible to tune the components of a circuit to maximize resonance with another circuit. The following references describe attempts to make use of circuit resonance for power transmission and related tasks.
U.S. Pat. No. 7,826,873, issued to Telefus, discloses a contactless energy transmission converter. This system wirelessly transfers energy from a source unit to a target unit. The source unit converts a current into a wireless signal. Preferably the source unit is coupled to a power source. The target unit is comprised of induction coils which generate electromagnetic fields, to pick up the signal and convert the signal into a current.
This system includes a transmitter configured to use a current to produce a wireless energy signal, and a receiver configured to convert the wireless energy signal into a current and charge a battery. A power source is coupled to a multiphase transmitter. The multiphase transmitter is coupled to a transistor pair. The transistor pair is coupled to the controller. A current emitted from the transistor pair is further coupled to a capacitor which in turn is coupled to a transmission antenna.
The contactless energy transmission converter operates when the power source supplies current to a multiphase transmitter which produces a first signal having a first frequency. The first signal is coupled to the transistor pair. The controller controls when the transistor pair is turned “on” and turned “off”. When the transistor pair is “on”, the first signal is allowed through the transistor pair and when the transistor pair is turned “off” the signal does not go through. As such, the controller is able to produce a square wave packet having a low frequency wherein the square wave packet frames the first signal having a first frequency, thus modulating the first signal. This modulated signal is then transmitted by the transmission antenna. The transmission antenna transmits the signal to the reception antenna of the receiver. The reception antenna is coupled to a DC-Converter which converts the signal into a DC current. The DC current is then used to charge the battery.
U.S. Pat. No. 7,521,890, issued to Lee et al. is directed to a system and method for selective transfer of radio frequency power. This process of wireless power transfer occurs between a primary unit and a secondary unit. The primary unit converts the DC power supplied by a conventional DC power supply connected to an AC outlet to a multitude of radio frequency oscillations. The various RF oscillations can be of different RF frequencies, or they could all have the same frequency. The RF signals are used to drive a set of primary coil arrays which are in general two dimensional in nature to generate inductive magnetic field above a substantially laminar surface in which the primary coils are embedded. When a device with a device adapter equipped with one or more secondary coils which can resonate with the inductive magnetic field excited by the primary coils, the RF power is transferred from the primary unit to the secondary unit by a RF cable. The transferred RF power is subsequently conditioned and rectified by the rectification circuit within the secondary unit into a regulated DC power with a substantially constant voltage. The regulated DC power is then used to power the device to perform such tasks as charging a secondary battery, or to be used directly by the device to power its electronics, etc.
The primary unit comprises a two-dimensional array of primary coils and attendant matching capacitors as well as the power rails for connecting the primary coils and capacitors to the primary RF power supply.
A compatible secondary unit sits on top of the primary surface, the parallel LC resonance frequency is shifted away from the driving frequency of the RF source, which, in turns, causes the effective local LC impedance to decrease sufficiently to enable the load current to flow into the local LC network. The receiving coil in the secondary unit likewise has a compensating capacitor in parallel with the receiving induction coil. The act of bringing the secondary unit close to one or more of the local LC networks of the primary unit, the inductive coupling is established between the primary unit and the secondary unit. This mutual inductive coupling creates a new local resonance substructure with its own resonance and anti-resonance frequencies.
Each capacitor is in series with a MOSFET switch which can be turned on to enable the capacitor it is directly connected to, or to turn off to disable the capacitor. Since each
MOSFET switch can be either ON, or OFF, the switched capacitor bank can provide different capacitance values which are more or less linearly distributed with values from 0 pF to 1,500 pF. The capacitance values are not precise because of the inherent variation of stock capacitors as well as the source drain capacitances of the MOSFETs. The source drain capacitance of the MOSFET is unimportant when the MOSFET is ON. However, when MOSFET is OFF, the capacitor it is connected to is not completely disabled because of the source drain capacitance which is in series with the external capacitor. The source drain capacitance of the MOSFET is not a constant, either, but depends on the source drain voltage. Hence it would be difficult to modify the capacitance values of the external capacitors to compensate for the added OFF capacitances caused by MOSFETs.
U.S. Pat. No. 7,511,454, issued to Legg illustrates a battery label with wireless battery charging circuit. This system includes an inductor that may comprise a small number of circular turns of sufficient diameter to allow them to cover an area of approximately 18 to 20 square inches (i.e. a coil of a diameter for example between 4 and 5 inches). This design manifests itself as a suitably flat coil, and could easily be molded into a mat or into the base of a tray made of insulating material. Devices containing wireless rechargeable batteries to be charged could be placed onto the mat or into the base of a tray allowing energy would flow from the charging circuit to the wireless battery charged circuit by electromagnetic induction.
U.S. patent application No. 2010/0184371, published for Cook et al. disclose to transmitters for wireless power transmission. This system includes a transmitter for generating a magnetic field for providing energy transfer from an input power. A receiver couples to the magnetic field and generates an output power for storing or consumption by a device (not shown) coupled to the output power. Both the transmitter and the receiver are separated by a distance. The transmitter and receiver may be configured according to a mutual resonant relationship and when the resonant frequency of the receiver and the resonant frequency of the transmitter are matched, transmission losses between the transmitter and the receiver 108 are minimal when the receiver 108 is located in the “near-field” of the magnetic field 106.
U.S. Pat. No. 6,906,495, issued to Cheng et al. is directed to contact-less power transfer. This reference discusses a prior art inductive system that includes a multiple coil array. The primary magnetic unit consists of an array of coils. The secondary magnetic unit may consist of a coil. When the secondary magnetic unit is in proximity to some coils in the primary magnetic unit, the coils are activated while other coils remain inactive. The activated coils generate flux, some of which will couple into the secondary magnetic unit.
It is an objective of the present invention to provide a means for efficiently transmitting power through resonance across extended distances. It is a further objective to provide an apparatus having this capability that is safe to use and does not produce excessive heat. It is a still further objective of the invention to provide such an apparatus that can be easily and consistently manufactured at a low price. Finally, it is an objective of the present invention to provide a power transmission apparatus that is easily tunable to various frequencies, that is durable and simple to use.
While some of the objectives of the present invention are disclosed in the prior art, none of the inventions found include all of the requirements identified.